1. Field of the Invention
This invention relates to cold-curing mortar or concrete compositions useful as building and construction materials and more particularly, to mortar or concrete compositions which in the set state have excellent strength, water-proofness and water repellency as required for mortar or concrete and improved crack resistance and weather resistance under outdoor exposure conditions.
2. Background Art
Cement structures are generally defined as comprising as predominant components a calcareous material, that is, a raw material based on CaO units (e.g., quick lime, limestone, slaked lime, cement, calcium carbonate, etc.) and a siliceous material, that is, a raw material based on SiO2 units (e.g., silica, sand, blast-furnace slag, fly ash, etc.). The cement structures include Autoclaved Lightweight aerated Concrete which has been aerated to have a low specific gravity and cold-curing mortar or concrete compositions using crushed stone as the aggregate and requiring high strength.
For the Autoclaved Lightweight aerated Concrete, it is known in the art to add various silicones for the purpose of improving water repellency.
For example, JP-A 55-42272 describes the addition of dimethylpolysiloxane, amino-modified polysiloxanes, polyether-modified polysiloxanes, alkyl-modified polysiloxanes, epoxy-modified polysiloxanes, fluorinated polysiloxanes, α-methylstyrene-modified polysiloxanes and alcohol-modified polysiloxanes. JP-A 55-85452 describes the addition of methylphenylpolysiloxane and chlorophenylmethyl-polysiloxane. JP-A 55-90460 describes the addition of methyl silicone varnishes, phenyl methyl silicone varnishes, blends or copolymers thereof with other organic monomers or polymers, and silicone varnishes modified with alkyd, epoxy or acrylic resins. JP-A 57-123851 describes the addition of dimethylpolysiloxane, methylphenylpolysiloxane, methylhydrogenpolysiloxane or methylcarboxyl-modified polysiloxane, which has been emulsified with an anionic surfactant to improve its dispersion in slurry. JP-B 1-44673 describes the addition of siloxanes containing alkoxy groups; JP-B 1-58148 describes the addition of siloxanes containing alkyl groups; and JP-A 8-26811 describes the addition of silicone oils containing alkyl and alkoxy groups.
In the event of Autoclaved Lightweight aerated Concrete which does not require so high a strength, water repellency is improved by the internal addition of various silicones. In the event of cold-curing mortar or concrete using crushed hard sand stone or the like as coarse aggregate without blowing agents, the internal addition of silicone oil as water repellent, though somewhat effective for improving water repellency, has not been practically employed. This is because the internally added water repellent acts to inhibit hydrogen bonds between raw materials such as calcareous and siliceous materials, detracting from the strength which is the most important feature of mortar or concrete. It is thus a most common practice to apply a water repellent to the surface of mortar or concrete after shaping and setting.
However, the application of water repellent takes a certain time for coating operation and is uneconomical because of a loss of coating solution. Additionally volatilization of water repellent has negative impact on the environment. On the other hand, due to the widespread use of air conditioning systems, concrete often encounters an environment entailing a largely varying temperature difference between the interior and surface of concrete. There are increasing cases where cracks occur in concrete as a result of such temperature differences. Cracks on the concrete surface not only give rise to structural problems and act to degrade durability, but are also aesthetically undesirable. It is thus demanded to overcome this problem.